Localizing a short

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  #1  
Old 02-03-18, 08:52 AM
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Localizing a short

What would be the best way to localize a short in a group of outdoor driveway/tree lights? I have a total of 21 light "fixtures" outdoors on this particular group. Regular 120v - 17 are ground fixtures, 4 are up in trees. They are on an OUTDOOR timer which is ultimately controlled by an INDOOR switch. Typically the indoor switch always is set to on and the lights go on & off based on my outdoor timers setting. They have worked fine for years. Recently that is no longer the case - now when the indoor switch is on and the timer trips to turn the lights on it trips the circuit breaker. I was hoping it was something easy like a defective indoor switch so I tried changing it but it made no difference. Where do I begin to isolate the problem? Obviously the wiring is all underground, etc. Any helpful hints or suggestions to guide me in isolating where the issue might lie? There are some other indoor lights on that same circuit and as long as I keep the "master" indoor switch that controls the outdoor lights off those lights work fine and do not cause the breaker to trip.

One other point - I have changed numerous bulbs over the years - Originally they were all typical incandescent bulbs ranging from 60W variety for the ground fixtures to 150W floods for the tree lights. Never had the issue. Now they're comprised of a bit of a mix of the older incandescent bulbs (Higher wattages) and newer LED bulbs (lower wattage). The fact that the overall wattage is lower then it ever used to be makes me believe it's not an issue related to overloading the circuit but I mention it for completeness sake.

Thanks for any guidance.
 
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Old 02-03-18, 09:40 AM
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Do you know or can you figure out the precise routing of wires from one fixture to the next outside (and from one outlet box to the next inside)?

Test 1. Remove all the light bulbs and unplug everything from receptacles on the circuit. Turn on the power. If the breaker still trips then skip to Test 2 below. Otherwise replace light bulbs one at a time starting at the beginning of the circuit (receptacle or light closest to the breaker along the route) and try the breaker again.

Test 2. Label and unhook the wiring in one place approximately in the middle of the route. Turn on the power. If the breaker still trips then the problem is in the half closest to the breaker (first; upstream). Then unhook the wiring in a location approximately in the middle of the first half. Turn the power on again.

If the breaker did not trip during the immediately preceding power-up then unhook the wiring in a location approximately in the middle of the second half and reconnect the wiring you unhooked earlier. Turn the power on again.

This helps you narrow down on the location of the problem.
 
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Old 02-03-18, 09:44 AM
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Do you have a multi meter or circuit tester?

Without a meter or tester I would disconnect each of your lights from the circuit one at a time. Try turning on the lights after removing each light. Once you've removed the problem fixture the breaker should no longer trip. This method will only help if the problem is in one of the fixtures. If you go through disconnecting all your fixtures and the circuit still trips then the short lies somewhere else like your wiring, timer or switch.
 
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Old 02-07-18, 07:21 AM
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So a follow up to more prior post.

I checked the main switch - works fine
I checked the wiring just beyond the timer - it works fine

Just after the timer the line i"splits" to supply to separate sets of lights (they used a three wire cable (white/black/red) to accomplish this - the black supplies one set of the outdoor lights the red a different group. When I "remove" the red wire from the pigtail the group of lights controlled by the black wire work fine so obviously the problem is in the wiring/other set of lights supplied by the red wire. I then individually removed each of the five lights in this grouping from the "circuit" and the breaker would still trip even when everyone of these lights was no longer connected. So at this point it makes me think there can be some sort of break in the underground wiring.

I'm not sure the order in which these five lights are connected from the start point. What would be a good way to test "continuity" from Point A (where the red wire starts at the pigtail) to each fixture. And then from fixture to fixture. Perhaps if I could figure out the "chain/order' of the fixtures I could isolate where the break might be rather then dig up a lot of ground.

If the fixtures are all disconnected and no wires touching, etc would you still expect the circuit to trip the breaker if the issue was a fixture problem and not a wiring problem? Thanks
 
  #5  
Old 02-07-18, 07:33 AM
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You could do this:

Turn off the power.

At each fixture label and unhook both the incoming hot wire and continuing hot wire (some may be black instead of red).

Test for continuity or resistance between each end of each hot wire and the white wires (the latter still hooked up). Continuity (near zero resistance) indicates a point of interest. If you do get continuity you would expect to get it twice which would be expected to be both ends of a wire where a short exists.

Remove the light bulbs (again).

If you tested for continuity between the empty hot terminal (you unhooked the wires earlier) and the white wire(s) and got near zero resistance then there would be a short in that fixture.
 
 

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